C. difficile Testing
Clostridioides (Clostridium) difficile Toolkit for Long-term Care Facilities

Recommendations for long-term care facilities

On this page:
Lab tests
Stool samples
Colon examination

Clostridioides (Clostridium) difficile infection (CDI) may be suspected in residents with new onset of diarrhea who have 3 or more unformed stools (conform to the shape of the container) in a 24-hour period. To determine if a patient has CDI, consider both clinical symptoms and lab test results.

Facilities can use multiple tests to confirm or to assist in confirming CDI in symptomatic patients. However, it is important to know what test is being used because they have widely varying turn-around times, sensitivities, specificities, positive predictive values, and negative predictive values.

Lab tests

• Culture
  • Most sensitive test available, but often associated with false-positive results due to presence of non-toxigenic strains
  • Labor intensive and requires careful laboratory quality control
  • Results are available within 48-96 hours
• Antigen Detection
  • Detects the presence of C. difficile antigen (GDH) by latex agglutination or immunochromatographicassays
  • Rapid test results (<1 hr)
  • Should be combined with toxin testing to verify diagnosis
• Toxin testing
  • Enzyme immunoassay (EIA) detects toxin A, toxin B, or both A and B
  • Same-day results
  • Easy to use
  • Low labor costs
• Polymerase Chain Reaction (PCR) / Nucleic Acid Amplified Test (NAAT)
  • Detects toxigenic C. difficile in stool
  • A potential advantage is ability to determine strains, for instance, whether they make toxin and to which toxin type they belong
  • A more sensitive and more specific approach

Stool samples

A C. diff stool culture is a specific kind of culture that is different than the typically requested bacterial stool culture. The culture has to be grown in an anaerobic environment, making it more labor intensive with a relatively slower turn-around time.

Before submitting a sample for C. diff testing, consider other causes of loose stools. This could include medications (stool softeners or proton pump inhibitors) or underlying conditions such as Crohn’s or bowel surgery.

Obtaining stool samples

• Only unformed stools should be tested (Bristol stool chart types 5-7). Testing asymptomatic residents (those with formed stools) is not recommended. Testing formed stools can lead to detecting colonized, not infected, cases. Since all positives must be reported to NHSN, this can lead to over-reporting CDI.
• Fresh stool is required.
• C. difficile toxin is very unstable and degrades at room temperature in as short as two hours. False negative results occur when specimens are not kept refrigerated until testing can be done.
• Collect specimen in clean, watertight container.
  • Transport media is not necessary and may increase false positive results.
  • Transport specimens as soon as possible and store at 2 - 8 °C until tested.
  • Storage at room temperature may decrease the sensitivity of some tests, possibly due to toxin inactivation.

Testing recommendations for stool collection and submission

Specimen rejection criteria for C. difficile toxin in stool samples

Colon examination

In some cases, examination of the colon can be used to help confirm a diagnosis of CDI. If C. difficile colitis is not accompanied by pseudomembrane formation, endoscopic findings are relatively nonspecific, but a biopsy specimen may reveal changes typical of pseudomembranous colitis.

Endoscopy

• Pseudomembranous colitis can only be diagnosed by direct visualization of pseudomembranes on lower gastrointestinal endoscopy
• At least 90% of patients with pseudomembranous colitis demonstrate either C. difficile or its toxin in stool samples
• Because of its cost, risk to the patient, and the availability of other diagnostic tests, endoscopy is usually reserved for special situations
• The American College of Gastroenterology Guidelines recommend endoscopy for situations such as the following:
  • a rapid diagnosis is needed and test results are delayed or insensitive tests are used
  • the patient has an ileus and stool is not available
  • other colonic diseases that can be diagnosed with endoscopy are being considered

Imaging tests

• Computerized tomography (CT) scan
  • Provides detailed images of the colon
  • This scan can show a thickening of the wall of the colon, which is common in pseudomembranous colitis

Sensitivity and specificity of diagnostic laboratory tests for CDI

*Sensitivity of a test indicates the probability that if the person has the disease, the test will be positive.
**Specificity is the probability that if a person does not have the disease, the test will be negative.

References

1. Cohen SH, Gerding DN, Johnson S, et al. Clinical Practice Guidelines for Clostridium difficile
Infection in Adults: 2010 Update by the Society for Health care Epidemiology of America (SHEA) and the Infectious Diseases Society of America (IDSA). Infect Control Hosp Epidemiol. 2010 May;31(5):431-55.
2. Mandell GL, Bennet JE, Dolin R.  Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases Seventh Edition. Philadelphia: Churchill Livingstone Elsevier, 2010.
3. Bartlet JG. Detection of Clostridium difficile Infection. ICHE. 2010; 31(S1):S35-S37.
4. Gerding DN, Johnson S, Peterson LR, et al. Clostridium difficile-associated diarrhea and colitis. ICHE. 1995;16:459-477.